476 GRAMINE^. TRUE GRASSES 



they are solid : maize is exceptional in having stems solid 

 throughout. 



Branches arise only in the axils of the lowermost leaves. 

 ' Tillering ' is the term employed to designate this form of branch- 

 ing in grasses, and its nature is discussed on pages 482-485. 



Generally the buds break through the base of the enclosing 

 leaf-sheaths ; the branches produced are designated extravaginal 

 branches and grow more or less horizontally for a time, often 

 underground, forming longer or shorter rhizomes, from which 

 leaves and flowering stems are sent up. Grasses behaving in 

 this manner soon cover considerable areas of the ground with a 

 close turf Couch-grass, smoothed-stalked meadow-grass, and 

 florin are good examples. 



Less frequently the branches are intravaginal, that is, they 

 grow up between the leaf-sheath and the stem, emerging near 

 the ligule, but ultimately, tearing the subtending leaf, as in i, 

 Fig. 153. Branching of this character leads to the formation of 

 compact tufts, and grasses exhibiting this manner of growth are 

 unable to cover the ground except in isolated patches. The 

 cereals (see pp. 482 to 485), annual brome-grasses, meadow and 

 sheep fescues, rye-grasses, and cocksfoot are examples. 



The perennial rhizomes of grasses are usually sympodia 

 (2, Fig. 22). 



Leaf. — The leaf of a grass consists of two parts, the blade 

 and the sheath. The leaf-sheath surrounds the stem like a tube 

 split down one side, its free edges overlapping in some instances 

 (^,Fig. 149). In cocksfoot, dodder-grass, and some of the meadow- 

 grasses it is not split but forms a completely closed tube. It acts 

 as a support for the stems while they are young and soft, and 

 protects the tender growing points within from the injurious 

 effects of frost and heat. Most grasses appear swollen at the 

 nodes {d. Fig. 149); this is not usually due to thickening of the 

 stem, but to the presence of a mass of soft tissue at the base 

 of the leaf-sheath. 



